Found the problem, after I replaced D1. Was still seeing excessive voltage on that rail. Upon closer inspection with a magnifying glass, there was a hairline separation in the trace between R2 and D2. So the diode was effectively out of the circuit. Used a thin piece of wire to reinforce that trace, and all's well!
Finally got this thing on the bench! (Busy...busy...busy....)
I have the schematic, but I'm having a little trouble locating where the supply voltage gets regulated down to +/- 10VDC. I can see the +/- 30VDC off the main supply.
Also, my pdf of the service manual doesn't have a very clear image of the main pcb. Any idea where I can find one?